Conventionally, laser diodes have been widely used in various fields. In a laser diode, induced emission is caused in an emission layer (active layer) that is interposed between a p-type region and an n-type region, and light generated thereby is extracted.
More specifically, light emitted by electrons, which have high energy and return to a low energy state, is reflected inside the emission layer using a mirror formed by cleavage planes or the like to promote induced emission. By repeatedly reflecting the light, intense light having a uniform phase is generated and extracted as laser light. Also, current continuously flows through a PN junction and laser light is continuously extracted.